Reactive magnesium oxide has numerous applications in industry and commerce, such as in animal feed additives, fertilizers, and flue gas conditioners. For such exemplary applications, a free flowing material with a specified particle size and chemical purity is demanded, having a surface area of at least 10 square meters per gram or higher, but preferably twenty square meters per gram or higher.
Typically, highly reactive magnesia is produced by reacting magnesium chloride solutions, such as derived from sea water or magnesium chloride brines, with lime (CaO) or a dolomitic lime (MgO:CaO) to precipitate insoluble magnesium hydroxide, [Mg(OH).sub.2 ]. The magnesium hydroxide is then calcined to the desired reactivity in a rotary kiln. The magnesium oxide product is often difficult to handle due to its poor flow properties and fine particle size, greater than 98% usually passing through a 200 mesh screen.
For most of its industrial applications it is desirable to employ a reactive magnesia having a relatively large particle size in order to minimize dusting. Other advantages for the larger particle size include ease of handling and ease of blending with other materials such as fertilizers. However, a satisfactory granulation process has yet to become known which does not involve substantial slaking of the magnesia, thereby altering the chemical reactivity and purity, and reducing magnesium value of the product.
U.S. Pat. No. 3,748,282 to Evans, for example, teaches producing magnesium oxide compositions in shaped forms, such as tablets and pellets, by slaking a quantity of particulate magnesium oxide with an aqueous solution containing from about 10 to 70% by volume, of a volatile, water miscible alcohol or ketone, thereby converting between about 30% to about 85%, by weight, of the magnesium oxide to magnesium hydroxide. The slaked mixture is then sequentially dried, granulated, shaped and calcined to convert a proportion of the magnesium hydroxide back to magnesium oxide, so that the shaped composition contains about 35% to about 55%, by weight of magnesium hydroxide. The total content of organic compound in the slaked mixture is completely vaporized during the drying and calcining operations. However, the very high proportion of magnesium hydroxide in the shaped product makes it unsuitable for any application requiring highly reactive and chemically pure magnesia.